CVE-2026-77540 in UniFi OS Server
Summary
by MITRE • 08/26/2026
A malicious actor with access to the network and high privileges could exploit an Improper Input Validation vulnerability found in UniFi OS Server to execute a Command Injection on the host device.
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Analysis
by VulDB Data Team • 08/26/2026
The identified vulnerability represents a critical security flaw within the UniFi OS Server architecture, specifically categorized as an improper input validation issue that facilitates command injection attacks. This type of weakness typically arises when software fails to adequately sanitize or validate user-supplied data before processing it through system-level interpreters such as shell commands. In this specific context, the vulnerability allows a malicious actor who has already established network access and possesses high privileges within the UniFi ecosystem to inject arbitrary operating system commands into the host device running the UniFi OS Server. The severity of this flaw is significantly amplified by the prerequisite requirement for high-level administrative credentials or equivalent privilege levels, which suggests that the attack vector targets trusted entities rather than unauthenticated external attackers. However, in environments where insider threats exist or where credential theft has occurred via other vectors such as phishing or lateral movement from a compromised endpoint, this vulnerability provides a direct path to full system compromise.
From a technical perspective, command injection vulnerabilities occur when an application constructs operating system commands using unsanitized input parameters without proper escaping of special characters that hold significance for the shell interpreter. For instance, if the UniFi OS Server accepts configuration inputs or API payloads and passes them directly to underlying Linux-based services without rigorous validation, an attacker can append malicious commands using delimiters such as semicolons, ampersands, or pipes. This exploitation technique aligns with Common Weakness Enumeration identifier CWE-78, which describes improper neutralization of special elements used in an operating system command. The presence of this flaw indicates a failure in the application's security design to implement strict allow-listing of acceptable input formats or robust encoding mechanisms that prevent the shell from interpreting injected payloads as executable instructions rather than data strings.
The operational impact of successfully exploiting this vulnerability is severe, resulting in arbitrary code execution with the privileges of the UniFi OS Server process. Since administrative accounts often run services with elevated permissions to manage network infrastructure components such as switches, access points, and controllers, a successful command injection could allow an attacker to read sensitive configuration files, exfiltrate cryptographic keys, modify firewall rules, or install persistent backdoors on the host system. This effectively breaks the isolation between the management plane and the underlying operating system, granting the adversary complete control over the network infrastructure's core components. Such access can be leveraged for further lateral movement within the corporate network, enabling the attacker to pivot from the UniFi OS Server to other critical assets that rely on authentication services or network policies managed by this platform.
This vulnerability maps directly to several techniques in the MITRE ATT&CK framework, particularly T1059 Command and Scripting Interpreter, which covers the execution of commands via shell interpreters like bash or sh. Additionally, it relates to T1136 Create Account if the attacker uses the injection to create new administrative users for persistence, and potentially T1078 Valid Accounts if high privileges were obtained through credential theft prior to exploitation. The scenario described highlights a classic privilege escalation path where initial access is gained through compromised credentials, followed by abuse of system functionality due to insufficient input validation. To mitigate this risk, administrators must ensure that all UniFi OS Server instances are updated to the latest patched versions released by Ubiquiti Inc., which likely include code changes to enforce stricter input sanitization and parameterized command execution practices. Furthermore, network segmentation strategies should be employed to restrict access to management interfaces only from trusted administrative subnets, reducing the attack surface available to potential adversaries who might gain initial footholds elsewhere in the network. Implementing multi-factor authentication for all administrative accounts adds an additional layer of defense against credential-based attacks that could precede this exploitation attempt.